Due to dramatic advances in semiconductor industry technology, it is possible to manufacture liquid crystal display devices (LCDs) that are high-performance as well as compact and lightweight. Cathode ray tubes (CRTs) have been widely used as information display devices. However, CRTs have a number of drawbacks in terms of miniaturization and portability, despite their advantages of low cost and high performance.
LCDs have entered the spotlight as an alternative display device that overcomes the disadvantages of the CRT. Among the advantages of the LCD are its small size, low weight, and low power consumption. Today, the LCD is provided with almost all information processing equipment that requires a display device.
The LCD displays images using modulation of light generated by a liquid crystal cell. That is, a predetermined molecular arrangement of liquid crystals is converted to another molecular arrangement by applying a voltage to the liquid crystal cell. Light is emitted from the liquid crystal cell by the converted molecule arrangement. The LCD displays images by converting optical characteristics of the liquid crystal cell such as double refractivity, optimal rotary power, dichroism and light scattering characteristics into visual variations.
An LCD is manufactured by forming a gate line, a data line and a TFT on an array plate, forming R, G, B color filter layers on a color filter plate, aligning the color filter plate on a glass plate to be placed in opposition to the array plate, cohering the array plate and the glass plate, and injecting liquid crystals between the plates.
The array plate and the color filter plate in particular are formed by sequentially performing a plurality of mask processes.
In a mask process, an insulating layer or a metal layer is deposited on the entire surface of the glass plate using a chemical vapor deposition (CVD) or a sputter deposition method.
After deposition of the layer onto the plate, the surface of the deposited layer is cleaned and a photoresist layer is coated onto the surface. After coating, the photoresist layer is patterned by an exposure and development process using a mask.
The deposited layer is selectively etched using the patterned photoresist layer as a mask, and then the patterned photoresist layer is eliminated. By eliminating the patterned photoresist layer, a single mask step is completed.
FIG. 1 illustrates an exposure method used in a manufacturing method of an LCD according to a related art.
As shown in FIG. 1, four active array plates are formed on single glass plate in (a).
That is, four active regions corresponding to four liquid crystal panels are formed simultaneously on the glass plate. After forming the four active regions, a cell process is carried out for dividing the glass plate into single active region units.
The process of forming the four active regions on the glass plate includes, for each of the four active regions, a first mask step of forming a gate line and a gate electrode, a second mask step of forming a channel layer, a third mask step of forming source/drain electrodes, a fourth mask step of forming a contact hole in a passivation layer, and a fifth mask step of forming a pixel electrode.
An exposure process is performed for the four active regions in each of the mask steps.
When the first mask step is carried out, a metal layer is deposited on the glass plate and a photoresist layer is coated on the metal layer. After coating, an exposure process is carried out using a mask pattern. The exposure process is performed four times on each active region sequentially.
In the exposure process, a single active region can be completely exposed by a one-time exposure process.
As shown in (b) of FIG. 1, one active region is formed on a glass plate in the case of a large LCD. In this case, a mask process cannot be completed with a single exposure process.
Since manufacturing costs increase in proportion to the size of the requisite exposure lens, a partitioned exposure process may be performed to reduce the manufacturing costs.
As described above, the partitioned exposure process completes a single mask process by performing a plurality of partitioned exposures on single active region. In contrast, the concentrated exposure process completes a single mask process by exposing an entire active region with a one-time exposure. One or the other of the partitioned exposure process and the concentrated exposure process is selectively used in manufacturing LCDs.
FIG. 2 illustrates overlapped exposure regions when a partitioned exposure process is performed.
Referring to FIG. 2, when a plurality of partitioned exposure processes are performed on one active region as shown in (b) of FIG. 1, an overlapped exposure region may occur at a boundary portion between the partitioned exposure regions due to, for example, a defective alignment between the mask and the glass substrate, a tilted exposure device, or the like.
As shown in FIG. 2, the partitioned exposure process includes a first exposure that exposes an active region within a predetermined width from a left edge of an active region formed on a glass plate. By the first exposure, a first exposure region is formed on the active region. After performing the first exposure, a second exposure is carried out on an adjacent active region to form a second exposure region. When the second exposure is carried out, an overlapped exposure portion is formed at a boundary region between the first exposure region and the second exposure region.
FIG. 3 illustrates a line failure generated when a partitioned exposure process is performed.
Referring to FIG. 3, when an overlapped exposure region occurs as shown in FIG. 2, a line width at the first and second exposure regions is formed to be larger than that at the overlapped exposure region.
In this case, the line resistance is undesirably increased.
Also, when the line is a pixel electrode or a common electrode, the storage capacitance determined by the gap between electrodes is undesirably changed, thereby degrading image quality.
Moreover, a line pattern failure due to the overlapped exposure causes stitches in the active region or a short circuit due to a reduced process margin.